This invention relates in general to Magnetostatic Wave (MSW) Resonators and relates more particularly to an MSW resonator having designed in suppression of spurious modes. In U.S. Pat. No. 4,528,529 entitled MAGNETOSTATIC WAVE RESONATOR issued to Ernst Huijer on July 9, 1985, an MSW resonator is presented in which a rectangular block 12 of yttrium-iron-garnet (YIG) film is positioned between a pair of microstrip conductors 11 and 13 that function as input and output transducers of the resonator. A magnetic field is applied to the block of thin film by a pair of magnetic poles 14 and 15. This resonator is illustrated in FIG. 1. In response to an oscillatory input signal in the input transducer 11, magnetostatic waves are launched in the rectangular block 12 of YIG film and induce in the output transducer 13 an output signal. The waves reflect from the ends and sides of the rectangular block of YIG film, producing constructive and destructive interference patterns that result in resonant responses in the output transducer.
In general, resonance modes will result at those frequencies for which there is an integral number m of half wavelengths in an x-direction perpendicular to the transducers and an integral number n of half wavelengths in a y-direction parallel to the transducers. Typically, it is desirable in a resonator to have only a single resonance mode coupling the input transducer to the output transducer. In the resonator presented by Huijer, all but the dominant modes are suppressed by spacing them away from the resonant cavity in either the x or y directions. However, such spacing reduces the coupling of the transducers to the magnetostatic waves in the block of YIG film, thereby reducing the transfer coefficient between the input and output transducers. In addition, there is only a small reduction in the nondominant (i.e., spurious) modes. Therefore, a more effective manner of spurious mode suppression would be advantageous.
SUMMARY OF THE INVENTION
In accordance with the illustrated preferred embodiment of the invention, a magnetostatic wave (MSW) resonator of the type developed by Huijer is presented in which spurious modes in the MSW resonator are suppressed by carefully selecting the locations of the input and output transducers. These transducers are selected to be substantially centered on one of the peaks of the selected resonant mode. These locations are also preferably selected to be located away from the peaks of the lowest order spurious modes.
Further spurious mode suppression is achieved by careful placement of one or more grooves in the surface of the YIG film. In general, the location of each groove is selected to substantially center that groove over a peak of the spurious mode that is to be suppressed by that groove. The width and depth of each groove is also adjusted to optimize the suppression of the spurious modes.